My 87t2 runs great, but only gets 4psi boost and sometimes less, could it be cats? I have both stock cats they look older. The car has 170k I just bought it 6months ago and I diconnected the air pump so I could go dual alt pulley, because I kept thowing belts.
I was going to get the cats removed for a hi-flow cat, is this a good idea? And should I hook the air pump back up with the new cat?

Thanks

 

wow...170K! is that on the original motor still? i'd also suspect the cats as the culprit of lower boost...has the turbo ever been rebuilt? does it still spool up around 2500 and not smoke at all?

 

There are only a few things that can cause low or erratic boost conditions - if you really want, I can dig up my big boost control review and troubleshooting "article" posted to the FCs mailing list.

In short, you're looking for
- intake restriction
- have you checked your air filter?
- are your intake hoses collapsing?
- YOUR THERMOWAX SYSTEM MAY BE STUCK SHUT (this prevents the secondary throttle plates from ever opening)
- exhaust restriction
- clogged cats (VERY LIKELY)
- clogged muffers
- bad turbo
...and a few other, less likely things.

Good luck!
Brandon

 

Not sure on motor I suspect a reman. Mufflers cat back looks new (stock replacement) I put an inbox K&N last year I ran a 14.94 et. with no air pump. But now it doesn't seem as peppy. And there is no smoke! The turbo doesn't seem to spool up quick anymore. All the intake pipes are good , some look brand new. The kid I bought it off of did not know sh.t. so I have to figure it all out.

thanks again. Jim

 

Hey, No7Yet*****
Any way you can find that article regarding low boost. I would appreciate it. Let me know. Thanks

 

You probably have clogged cats. Disconnecting the airpump can cause the main can to clog....on top of that you have 170K miles on them which may have clogged them already anyway. I have an '87 TII with 230K miles and a new engine. I had boost problems in the past. Found the following:
Cracked TID
Leaking Intake Gasket
Disintegrated Pre-Cat
Partially clogged main-cat
Malfunctioning boost gauge

I repaired all those things and now it boost all the way to the +sign on the gauge. My car is still on the original turbo and it works great....does not even smoke.

Todd

 

Here it is:

---
From: Brandon Matthews <bmatt@d...>
Date: Sat Mar 30, 2002 3:20 am
Subject: Re: [fc3s_org] Can anyone explain turbo control system?

I'm going to add to what Dale wrote, and try my best to write it as to
be applicable to both S4s and S5s, and the problems all us TII owners
seem to have :-)

The factory boost control system makes use of several things. The
biggest "boost controller" is intake/exhaust restriction. The stock
intake setup sucks, frankly, with an MAF and the super-sucking turbo
inlet ducting. The stock exhaust isn't really much better; there's a
turbo sized for low lag (and thus, too small), three cats, and some
pretty restrictive mufflers. Ugh. These things alone control boost a
good deal, by reducing the overall amount of air that can reach the
engine.

- If your cats clog up, or your intake gets clogged (have you checked
your air filter lately?), it reduces the efficiency of the whole system.
Low boost, since less air can reach the engine, or air "backs up" in the
exhaust, slowing down both how fast and how much air passes over the
turbine.

In S4 cars, Mazda tried implementing what they called a "dual scroll"
turbo system. Basically, there are two paths that S4 cars' exhaust
gasses can pass through, on their way to the turbine. Each "attacks" the
turbine wheel at a slightly different angle, with the "first" angled for
fast response (no lag), and the "second" for good flow. It's controlled
by a little "flapper" that almost-completely switches between the two
"angles". The "first" is enabled when the engine sees under a certain
amount of boost (er, atmospheric, maybe? not sure). When the car hits
boost, (like the wastegate actuator) a little rod gets pushed, and the
flapper moves, "freeing" up the exhaust path.

- While I don't know for sure, failure of this system seems rather
common. Guess what would happen if the flapper got stuck in the "no
boost" position? Nope. Guess again. Okay, yeah, you'd get... Low boost!
(what a shock) It can be removed, with great success. Ask RETed about
it; I dunno :-) I'm an S5 guy.

The throttle body, however, is where the real "action" happens. The
throttle plates control how much air goes into the engine, and thus how
much air passes over the turbine (exhaust side of the turbo). (Simply,)
The amount of air that passes over the turbine controls how fast the
turbo spins, which directly controls how much air is forced into the
engine - "boost". The more air that passes over the turbine, the faster
the assembly spins, and the more air that is compressed.

- The stock thermowax system has a few uses. It keeps your idle high
when the engine's cold, to help warm it up faster. It also keeps your
secondary throttle plates closed, to, in effect, "keep the throttle
closed" at least partly. This keeps boost down for the dumbkapfen who
gun it when cold. This gets sticky, and prevents those plates from ever
opening fully, with _no_other_side_effects_. What happens when you can
only ever open your throttle plates 1/3 of the way? You guessed it - low
boost. It don't even feel wierd through the pedal; you'd never know it
was happening. How to fix? Do the throttle body mod, goddamnit! :-)

The stock wastegates control what is a positive feedback system. ALL
years are sprung at ~5.5 lbs. On the S4s, there is a line that goes
directly from the compressor outlet to the wastegate actuator. On the
S5s, there's a tee in this line, which leads to the "Duty Control
Solenoid" (Mazda's name) - it's essentially a factory boost controller.
As what Dale said, wastegates bypass exhaust gases around the turbine,
to control the its speed.

- Well, I've never heard of it happening, but I supposed it could... The
wastegate could get "stuck" open, preventing the turbo from ever
reaching full speed. Guess what? Low boost. This would have the "odd"
symptom of causing boost to be "stepped". You'd only get about 2 lbs in
1st, 3 in 2nd, 4 in 3rd, and maybe 5 or 6 in 4th. Like I said, it's
rare, but possible.

Boost controllers work by bleeding off presure from this line, and thus
reduce the amount of boost "seen" by the wastegate actuator. That's how
the stock duty control solenoid works - it bleeds pressure off the
wastegate line at a controlled rate, in order to keep the wastegate
closed "just enough" so that the car can build 7.5 lbs of boost. Keep in
mind that ONLY 89+ cars have this.

- This little solenoid's pretty far out of the way, stuck to the oil
filler neck. Like everything else on the car, it seems, it's probably
prone to failure. If the little bugger never "opens", the wastegate
never gets "fooled", and opens at 5.5 lbs, just like the S4 cars. Viola,
low boost. Er, well, for S5s. S4s don't have this little bu- er,
"feature".

- Like I said, the speed of the compressor wheel determines how much air
is compressed, and thus, how much "boost" there is. If the turbo is
"bad", any number of things could unnaturally limit how fast the whole
deal spins. Guess what? Low boost.

The blow-off valve, doesn't really "control" boost, it just relieves it.
See, the throttle plates come "after" the compressor. When the throttle
plates snap shut (you drop throttle), the compressor is still happily
spinning along at 100,000RPM, compressing air like it should. But now it
has nowhere to go. Without a BOV, as it's called, all this air would
"bounce" back at the compressor, causing all sort of wierd harmonics and
vibrations, and slowing it down REAL fast like. This is, it would bounce
back over and over. Not good. So when there's vacuum after the throttle
plates, and boost before it, the BOV opens up and feeds this air back
into the "open air" side of the compressor. This both prevents the
compressor from "surging" (the bad stuff described above) and keeps it
spinning a while so after you get done shifting, it won't have to spin
up much to get you back in boost.

- Again, like the wastegate, I've never heard of a stock on failing, but
who knows? If the BOV sticks open, any pressure that the compressor
would try to stuff into the intake would be rerouted back around it.
Kinda like a boost leak, except that all the air's accounted for, so
there's no uglyness - just low boost.

- All of these bits are connected together by rubber hoses. Rubber hoses
get old and crack over the course of ~15-11 years. If one of these hoses
is bad, unmetered air gets in under vacuum (idle or dropped throttle).
This can cause a rough idle, a stumble, any number or problems. If
there's a major crack in a hose _after_ the compressor wheel, all the
pressure that the engine would see gets bled off to atmo. While I've
never seen that firsthand, I'd imagine that it would manifest itself at
a short rise in boost (maybe to 2-3 lbs), then a drop to atmospheric,
with a simultaneous but fairly short-lived overspin of the turbo, then
just plain low-to-no boost. Erg.

Holy CRAP! That was a freakin' diatribe! Listen, will someone save that
for future reference? I'm sure to lose it. Well, save it after it's been
corrected.

With all that said, is someone looking to hire a quick-learning,
fairly-hard-working 18 year old in Florida? I already know a good deal,
and I can web-monkey and do electronics stuff REALLY well, just not much
heavy stuff (I'm a pretty slight guy). Oh, and I like to fancy myself a
writer at times...

Anyway, hope that helps! Get to work, boys!
---

Perhaps this one can be archive? :poke: (moderators)

Brandon

 

The WATER THERMO VALVE, not the THERMOWAX, is the item that could cause the double throttle valve No.2 not to open. The thermowax effects the primary throttle valve during transition from a cold engine to a warmed up engine.

Saw that error twice in this thread and its misleading. I see visions of people removing the thermowax to correct a No2 secondary throttle valve from opening. Thats the only reason I mention it. Not carping or backbiting.

 

WOW!! THANKS GUYS. I'll check all that stuff and what I can't check I'll have checked. I think I'll get the cats done next week seeing as there so old looking. But do I need the air pump hooked up to an aftermarket cat ? And do you know how to check an aftermarket boost gauge for leaks ? Or a fancy way to check the intake pipes ?

Thanks , Jim

 

Note that I said "thermowax system". It's a general term that uses a well-known part to describe a common troublemaker.

Thank you.



...and besides, if one were going to remove the thermowax (i.e. doing the TB mod), why in the world would they not go "all the way"? Seems like a bit of a moot point to me.

Brandon

 

brandon, Love that don't fuc with the T2 saying. saying

 

I'd like to remove the thermovalve, just to be rid of any problems, but leave the thermowax so my car will idle when cold! Is that possible?

Todd

 

Yes, entirely. That's what I did. Just remove the second(first) set of throttle plates. Not to hard to do. Then JB weld the shaft hole. Do this carefully so it doesn't dislodge and get sucked into your engine.

S

 

Bolshoi. Just disconnect the vac hose going to the double throttle diaphram that comes from the Water Thermovalve if you want to assure the throttle plates open all the way.

Fact is you should just go out to your car and look at the throttle on its forward side. See the double throttle diaphram with the rod sticking out of it? See how that rod makes a 90 degree turn into a piece of linkage. That piece of linkage has a cruved slot in it that the rod rests in. If, after starting the car and its warmed up, the rod is at the bottom of the curved slot, then you might have a problem with the water thermo valve. If after warming the engine up the rod is at the top of the curved slot, the throttle plates are opening fully when stepping on the throttle.

All you have to do to disable the diaphram that controls the opening and shutting of the butterflys, is to go to the rear of the throttle body and find the row of four nipples for vacuum hose. The bottom nipple is the one that feeds the water thermo valve and from there the double throttle diaphram. Pull the hose off and put a cap on the nipple. A darn sight easier than screwing up your throttle body by taking the water thermo valve and thermowax off. Results in a crummy idle.

AKAGEALS.... Just remove the vacuum hose to the water thermo valve that comes from the throttle bodys lower nipple, and plug the hose or pull the vac hose off the bottom nipple on the back of the throttle body and cap the nipple. If the diaphram is disabled, the throttle plates will open.

 

Interesting.

There are other benefits to doing the TB mod, however, and fixing sticky secondary throttle plates is just one of them. Increased throttle response, a slight increase in power from increased airflow, elimination of the entire manifold coolant flow path, and better looks are the others. The TB mod was one of the best "free" mods I've done.

Oh, and a crummy idle? Perhaps if it's not adjusted correctly. In fact, the Pensacola RX-7 guys rib me about my idle - they say they're not sure it really is an RX-7, and that they've never heard an RX-7 idle as smoothly as mine. It's a definite improvement from the lumpy, inconsistent, and dashpot-softened crap idle I used to have. My car now sits at a SOLID 750 RPM when started stone cold, without ever having to touch the throttle. It just takes effort...

Brandon